Not a direct copy

Cross-posting Facebook to Instagram: what actually breaks

Not directly. Instagram will not accept a text-only post, so a straight copy is impossible — the post has to be rebuilt for Instagram, not forwarded to it.

Side by side

FacebookInstagram
Characters2,0002,200
Mediaoptionala photo or video (required)
Hashtags1-3 hashtagsmax 5 hashtags at the END of the caption
Links in bodyfinefine
Needs platform approvalyesyes

What changes, one by one

Instagram will not accept a text-only post

Facebook posts are frequently text-only. Instagram requires a photo or video on every post, so there is no direct equivalent — you have to attach media before this cross-post is even possible.

The hashtag rules are not the same

Facebook: 1-3 hashtags. Instagram: max 5 hashtags at the END of the caption. Carrying the tag block across is the single most obvious sign of an automated cross-post.

Why copy-paste cross-posting underperforms

Facebook is warm and community-toned; 40-80 characters peaks engagement. Instagram is built for short captions — under 100 characters is rewarded. Those are different jobs, so the same words cannot do both well — and every algorithm here demotes text that obviously was not written for it. The fix is not to skip cross-posting; it is to send a native version to each network.

Publish to both in one call

curl -X POST https://postwire.io/api/post \
  -H "Authorization: Bearer $POSTWIRE_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "platforms": ["facebook", "instagram"],
    "text": "Your post",
    "per_platform": {
      "facebook": { "text": "The Facebook version" },
      "instagram": { "text": "The Instagram version" }
    }
  }'

PostWire's /api/generate writes those per-platform versions for you from a single prompt, respecting every limit in the table above. From an AI agent it is one MCP tool call.

Get an API key free →

Questions people actually ask

Can I cross-post from Facebook to Instagram?
Not directly. Instagram will not accept a text-only post, so a straight copy is impossible — the post has to be rebuilt for Instagram, not forwarded to it.
What is the character limit difference between Facebook and Instagram?
Facebook allows 2,000 characters and Instagram allows 2,200.
How do I post to Facebook and Instagram at the same time?
With PostWire, one API call publishes to both: POST /api/post with platforms set to ["facebook","instagram"]. Or one MCP tool call from an AI agent.

Other pairs: Instagram to Facebook · all combinations · which APIs need approval